This project deals with the mechanisms involved in neural differentiation and neuron specification during development, and it also concerns the synpatic reorganization of transplanted eyes. The visual system of dipterans at different developmental stages has been selected as biological model because of its spatially ordered morphology and modular arrangement of most of its nerve connections. The principal and associated investigator have been working in this field since 1963. Different kinds of experimental manipulations can be performed in these animals at larval and pupal periods. These include microsurgery, laser microirradiation and transplantation of the eye anlage (eye-imaginal disks). It is also possible to obtain the differentiation of the eye-imaginal cells "in vitro". Using this material it isplanned to investigate the neural plasticity of the visual system analyzing by means of three-dimensional electron microscopy and Golgi techniques the reorganization of the nerve connections in transplanted and grafted eyes (see our enclosed paper (9)). It is also planned to continue our investigations on the neural differentiation of the eye-imaginal cells (7) studying by means of autoradiographic techniques the changes in DNA synthesis during the development of the disk. The formation of the fixed and characteristic cell patterns found in the adult eye will be also analyzed employing microsurgical techniques. In the same technical context we shall follow our studies concerning the propagation of the socalled neural differentiation wave (8).